The long-term objective of this project is to identify the mechanism of time perception. The ability to distinguish between time intervals is required for decisions, associations, memories, and other basic psychological processes. The specific aim of the proposed research is to determine if there is a substantial empirical basis to believe that oscillatory processes, rather than the accumulation process normally assumed by Scalar Timing Theory, are involved in timing stimuli in the second-to-minute range. Two series of experiments will be conducted with rats; with the bisection procedure, the range of times from 25 ms to 25.6 s will be explored for local discontinuities in the accuracy of time perception; with a random interval schedule of reinforcement, the range of times from 12.8 to 51.2 s will be explored for regularities in the search pattern. In the short term, the most likely application of the results is in the development of some simple noninvasive neuropsychiatric tests of time perception that will serve as an aid to diagnosis of several psychiatric disorders. In the long term, the value may be to increase understanding of the interrelationships between the biological bases of several psychiatric disorders.